The danger of nitrosamines is well known. Nitrosamines exercise an acute hepatotoxic action, and are carcinogenic, mutagenic and teratogenic. The presence of nitrosamines in dinitroanilines, even in quantities of a few ppm, is considered undesirable. Much effort has been directed to the removal of nitrosamines in dinitroanilines. See, e.g., U.S. Pat. Nos. 4,127,610; 4,185,035; and 4,226,789.
The removal of nitrosamines from dinitroanilines does not necessarily eradicate all residual nitrosating species. A dinitroaniline which shows only a negligible nitrosamine content may subsequently develop a higher nitrosamine level. This occurs if the dinitroaniline herbicide containing residual nitrosating agent is formulated with or exposed to secondary amines which may be, for example, either an impurity in the formulation or a naturally occurring amine.
Circumstances which favor nitrosamine formation present a problem. Processes to stabilize dinitroanilines against subsequent nitrosamine formation have been disclosed in U.S. Pat. No. 4,501,608 where a method of stabilizing dinitroanilines against the formation of nitrosamines by the incorporation of an addition compound comprising a bisulfite in conjunction with an aldehyde or ketone is disclosed. U.S. Pat. No. 4,440,962 discloses a process for obtaining dinitroanilines free from nitrosating agents by treatment of a dinitrochloro precursor to the dinitroaniline with an 1% to 5% aqueous bisulfite solution at a temperature of 50.degree. C. to 100.degree. C. and at a pH of from 1 to 3 for 1 to 3 hours.
Additionally, the presence of chloroaromatic impurities in dinitroaniline herbicides is problematic in that these impurities have been implicated as being responsible for a drop in pH upon formulation with other herbicides and bases such as ammonia.
It would be desirable to have a single process which would both reduce chloroaromatic impurities as well as stabilize dinitroanilines against subsequent nitrosamine formation.